"Compared with men, women utilize relatively more fat and less endogenous carbohydrate (CHOendo), but preferentially oxidize exogenous CHO (CHOexo) during exercise. As it has been demonstrated that pre- and early-pubertal children do not exhibit sex differences in substrate utilization, the adult phenotype is likely due to sex hormones. Whether sex influences substrate utilization during exercise in adolescents, in whom differences in sex hormones become larger, is unclear".

This study attempted to determine the influence of gender on endogenous and exogenous substrate utilization in healthy adolescent boys (N = 13) and regularly menstruating girls (N = 10). Ss cycled for 60 min at ~70% VO2max while intermittently drinking a 13C-enriched 6% CHOexo (4% sucrose, 2% glucose) solution (~1.5g/kg) in one trial (CT) or flavored water in another (WT). Both trials were completed by the girls within the follicular phase of their menstrual cycle. Respiratory exchange ratio and 13C/12C ratio in expired CO2 were determined during the last 15 min of exercise.

Respiratory exchange ratio was lower during in the water trial than in the carbohydrate trial, with no gender differences. CHOexo oxidation rates were similar between boys and girls, as was the % contribution from CHOexo to total energy yield and the oxidation ratio of CHOexo:CHOendo.

Implication. During adolescence, gender is not a major determinant of fuel selection during relatively high intensity exercise. One implication might be that adolescent boys and girls can equally derive metabolic and performance benefits from consuming CHO during competition.